A thick film circuit is suitable for many types of electronic equipment, such as broadcasting radio receivers, television receivers, video tape recorders, communication equipment, and measuring equipment.
Such a thick film circuit is generally formed using the screen printing method. More specifically, a desired pattern is formed on a substrate made of almina ceramic using a conductor paste, resistor paste and so on, followed by drying and heating so as to manufacture a thick film circuit. However, the screen printing method uses a mask pattern, with the result that a longer time is required for the exchange of mask pattern and cleaning of mask pattern and squeegee, and thus it is unsuitable for small lot production and frequent changes of the circuit formed.
On the other hand, a method which involves drawing on a moving substrate using a paste directly extruded from a nozzle without employing the mask pattern is reported in the "1978 International Microelectronics Symposium of ISHM, Minneapolis, MN, Sept. 17, 1978" and is introduced in the journal "Electronic Packaging and Production (January, 1981), Pages 98-109".
In operation, a drawing nozzle having a discharge hole for discharging a paste is kept at a certain distance from a substrate and is moved relative thereto to apply the paste for drawing a predetermined pattern of a thick film circuit. This drawing method does not require a mask pattern because the thick film circuit is drawn by means of NC control, thereby allowing the operator to quickly change the pattern and instantly modify the circuit.
However, one of problems with such a drawing method is that, when it is used to draw a continuous thick film circuit pattern having linear lines and curves, difficulty is encountered in drawing curve portions of the pattern at a high speed due to inertia of the drive system of the nozzle. Therefore, to efficiently form the thick film circuit by the above-described drawing method, it will necessary to draw linear portions at a high speed and curved portions at a relatively low speed. However, this technique does not produce satisfactory results because of the occurrence of variations in the film thickness and line width caused by the difference of moving speed of the nozzle between linear portions and curve portions. This problem will likewise be experienced in a method in which the substrate is moved without moving the drawing nozzle. Therefore, according to the conventional techniques, it is difficult to form the thick film circuit at a high speed and with high accuracy.